In the biopharmaceutical field, recent advancements in genetic engineering and cell culture technology have driven expression levels higher than ever, putting a considerable burden on down-stream purification, especially the capture step. While the introduction of new chromatography resins significantly improves the efficiency of a process based on a conventional fixed bed chromatography, additional gains can be achieved by operating in a continuous manner. The latter is especially appealing when continuous bioreactors, such as those operated in perfusion mode, are employed.
In continuous chromatography, several identical columns are connected in an arrangement that allows columns to be operated in series and/or in parallel, depending on the method requirements. Thus, all columns can be run in principle simultaneously, but slightly shifted in method steps. The procedure can be repeated, so that each column is loaded, eluted, and regenerated several times in the process. Compared to ‘conventional’ chromatography, wherein a single chromatography cycle is based on several consecutive steps, such as loading, wash, elution and regeneration, in continuous chromatography based on multiple identical columns all these steps occur simultaneously but on different columns each. Continuous chromatography operation results in a better utilization of chromatography resin, reduced processing time and reduced buffer requirements, all of which benefits process economy. Continuous chromatography is sometimes denoted simulated moving bed (SMB) chromatography.
Bisschops et al (“Simulated Moving Bed technology in Biopharmaceutical Processing”, Bisschops, M. and Pennings, M., Recovery Biological Products XI, (2003) Banff, Alberta, Canada) discloses a continuous chromatography method based on simulated moving bed (SMB) technology, which has been successfully employed for the laboratory scale purification of IgG with a protein A affinity resin. Despite the fact that the multi-column and multi-zone continuous approach provided by SMB greatly increases process efficiency, SMB systems have not been utilized to date for cGMP biopharmaceutical production, mainly because of system complexity from both hardware and operational perspectives.
Heeter et al (Heeter, G. A. and Liapis, A. I., J. Chrom A, 711 (1995)) has suggested, as an alternative to a typical four zone SMB system, a method based on a three column periodic counter-current chromatography (3C-PCC) principle. More recently, Lacki et al (“Protein A Counter-Current Chromatography for Continuous Antibody Purification”, Lacki, K. M. and Bryntesson, L. M., ACS (2004) Anaheim, Calif. USA) described the use of such a 3C-PCC system for IgG adsorption to MABSELECT™affinity resin. This 3C-PCC method requires simpler hardware and easier operation than the typical four zone SMB system, directly reducing the cost associated with the capital equipment and the maintenance of the system.
In fact, simulated moving bed technology has been utilised for decades in various other fields. For example, U.S. Pat. No. 3,291,726 (Universal Oil Products) described as early as 1966 a continuous simulated counter-current sorption process for the petrochemical industry.
U.S. Pat. No. 6,325,940 (Daicel) relates to a simulated moving bed chromatographic system comprising packed beds filled with separating fillers, by which the separation performance of the packed beds can be evaluated without removing the packed beds from the circular fluid passage. As the packed beds can be evaluated without removal thereof, the system can be examined on whether the deterioration of the system is caused by the columns or not, and, if yes, which column causes the deterioration. The system comprises at least four packed beds connected in series and endlessly to each other and ports for adding and taking out fluid.
U.S. Pat. No. 5,457,260 (UOP Inc.) relates to a control process for simulated moving adsorbent bed separations. More specifically, a process of continuously controlling at least one characteristic of a simulated moving adsorbent bed separation process is disclosed. The characteristics controlled may be the purity or the recovery of the component of interest. The process involves measuring the concentration of the components in the pumparound or pusharound stream, calculating the value of the characteristic, and making required adjustments to operating variables according to an algorithm which relates changes in the value of the characteristic to the changes in the concentrations of the components resulting from changes in the operating variables. Thus, the necessary quantity of data to control the separation is rapidly generated, thereby providing efficiency, precision and accuracy.
An essential factor for a reliable continuous process is the quality of the columns used, and more specifically the similarity or even identity between columns. If the columns are not identical, the theoretical calculations will not be correct, and it will become difficult to design an efficient and robust continuous chromatography process. Also, for scale-up considerations, having identical columns in the system is essential. However, the packing of a column with a chromatography media is very complex in order to obtain repeatable results. Even small differences in the number of plates or other packing properties can have a huge effect on the end result.
Pre-packed columns for large scale chromatography are available on the market. The advantage of pre-packed columns is that the supplier provides a column already packed with resin to the end user, whereby said user can include the column into a process without having to go through the relatively complex procedure of column packing However, for such columns to be useful in continuous chromatography; they need to be packed within very tight specifications. Such similar columns are available for analytical scale chromatography, and for small scale preparative chromatography. However, for large scale operation, there is still a need of pre-packed chromatography columns, which are provided with suitable means for connection to such a system, which columns are packed within tight specifications.
In the pharmaceutical industry, biomolecules, such as proteins, nucleic acids etc, are commonly separated by conventional chromatography using a single column. However, even though safety and quality issues may be easier controlled in a single column than in a more complex set-up, a common concern is the capacity obtained using such conventional chromatography. Thus, there is a need in this field of improved methods of chromatography, which improve the overall efficiency and economy obtained today with single column chromatography.